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High-Speed Magnets: Exploring Faraday's Law and Lenz's Law *

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Difficulty
Time Required Very Short (≤ 1 day)
Prerequisites This project requires a high-school level understanding of electromagnetism, or a willingness to learn about it.
Material Availability A kit containing the materials for this project is available from our partner Home Science Tools.
Cost Average ($40 - $80)
Safety Neodymium magnets must be handled carefully. Please see the detailed warnings in the Procedure.
*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.

Abstract

Safety Notes about Neodymium Magnets:

  • Handle magnets carefully. Neodymium magnets (used in this science project) are strongly attracted and snap together quickly. Keep fingers and other body parts clear to avoid getting severely pinched.
  • Keep magnets away from electronics. The strong magnetic fields of neodymium magnets can erase magnetic media like credit cards, magnetic I.D. cards, and video tapes. It can also damage electronics like TVs, VCRs, computer monitors, and other CRT displays.
  • Keep magnets away from young children and pets. These small magnets pose a choking hazard and can cause internal damage if swallowed.
  • Avoid use around people with pacemakers. The strong magnetic field of neodymium magnets can disrupt the operation of pacemakers and similar medical devices. Never use neodymium magnets near persons with these devices.
  • Use the magnets gently. Neodymium magnets are more brittle than other types of magnets and can crack or chip. Do not try to machine (cut) them. To reduce the chance of chipping, avoid slamming them together. Eye protection should be worn if you are snapping them together at high speeds, as small shards may be launched at high speeds. Do not burn them; burning will create toxic fumes.
  • Be patient when separating the magnets. If you need to separate neodymium magnets, they can usually be separated by hand, one at a time, by sliding the end magnet off the stack. If you cannot separate them this way, try using the edge of a table or a countertop. Place the magnets on a tabletop with one of the magnets hanging over the edge. Then, using your body weight, hold the stack of magnets on the table and push down with the palm of your hand on the magnet hanging over the edge. With a little work and practice, you should be able to slide the magnets apart. Just be careful that they do not snap back together, pinching you, once you have separated them.
  • Wear eye protection. Neodymium magnets are brittle and may crack or shatter if they slam together, possibly launching magnet fragments at high speeds.
In the Science Buddies project Human-Powered Energy, you can learn about the basics of magnetic induction, or how moving magnets can be used to generate an electric current. The detailed physics of how a changing magnetic field can induce an electric current are described by Faraday's law and Lenz's law (see the Bibliography for more information about these two laws). For a more advanced version of the Human-Powered Energy project idea, try setting up an experiment to prove or demonstrate these two laws, using the Shaking Up Some Energy Kit from our partner Home Science Tools. Since this is an abbreviated project idea, Science Buddies will not give you an exact procedure to follow. Instead, you will need to come up with your own hypothesis and procedure to test it. The suggestions below can help you get started.
  • Examine the equation form of Faraday's law, which states that the voltage generated in a coil of wire is proportional to the number of turns in the coil, and the rate of change of the magnetic flux. How can you manipulate either one of these two variables and measure the resulting change in voltage? Here are a few hints:
    • The rate of change of magnetic flux depends on how fast the magnets are moving through the tube. Rather than shaking the generator (which would make the magnets' velocity difficult to measure), construct a longer tube and drop the magnets through it from a known height, which should allow you to calculate their velocity when they pass through the coil.
    • In order to properly measure the voltage, you will need to use a multimeter set to measure AC voltage, or an oscilloscope. If you do not have access to either tool, you can use LEDs in series as a very rough measurement of the peak voltage (as described in the original Human-Powered Energy project idea). Keep in mind that voltages add in series, and the forward voltage drop of a red LED is roughly 2.2 V.
  • Lenz's law describes how the polarity of the voltage induced in a coil depends on the direction a magnet's poles are facing and the direction in which the magnet is moving. Connect two LEDs to your coil with opposite polarities, meaning the LEDs should be wired in parallel, but facing opposite directions—the anode (long leg) of one LED should be connected to the cathode (short leg) of the other LED, and vice versa. How can you use this configuration to demonstrate Lenz's law? When you shake the generator, will the LEDs flash at the same time, or will they alternate? Here are a few hints:
    • The timing of the LED flashes may be difficult to see with the naked eye. Many modern smartphones and digital cameras have a "slow motion" video capture option, which will record video at 60 or even 120 frames per second. Use this ability to film the LEDs as you shake the generator. Use a media player that lets you step through a video frame-by-frame to closely examine the timing of the LED flashes.
    • Construct the tube for your wire coil using a transparency sheet (available at Amazon.com or an office supply store) instead of cardstock. This will allow you to see the magnet moving inside the coil. Rather than shaking the generator with your hand, which would be difficult to film, set up a longer tube and drop the magnet through it from a known height. Set up your camera so you can film the magnet falling through the tube and see the LEDs flashing in the same frame, as shown in Figure 1. This will allow you to correlate the position and velocity of the magnet within the tube with the timing and brightness of the LED flashes. Do your findings match up with your predictions based on Lenz's law?
induction coil with magnet and LEDs
Figure 1. This experimental setup has two LEDs connected with opposite polarity, and a generator with a clear tube so you can see the magnets moving inside.

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Credits

Ben Finio, PhD, Science Buddies

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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Finio, Ben. "High-Speed Magnets: Exploring Faraday's Law and Lenz's Law." Science Buddies, 24 Apr. 2018, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p097/physics/high-speed-magnets-faradays-law-lenzs-law. Accessed 18 Aug. 2018.

APA Style

Finio, B. (2018, April 24). High-Speed Magnets: Exploring Faraday's Law and Lenz's Law. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p097/physics/high-speed-magnets-faradays-law-lenzs-law


Last edit date: 2018-04-24

Bibliography

To learn more about magnetic induction, Faraday's law, and Lenz's law, see the following website, or consult your high school physics textbook:

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Materials and Equipment Product Kit Available

In addition to the kit from our partner Home Science Tools, you will need some other materials to complete this project. Here are some suggestions based on Figure 1 from the Summary:

  • Transparency sheets, available from Amazon.com
  • Corrugated cardboard
  • Scissors
  • Craft knife or utility knife
  • Super glue
  • Tape
  • Fine-grit sandpaper (used to remove insulation from the magnet wire)
  • Smartphone or digital camera with slow-motion video capture mode

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